Rolls for corrugating metal strips



Nov. 6, 1956 A. G. GETZ ROLLS FOR CORRUGATING METAL STRIPS Sheets-Sheet l Original Filed March 23, 1951 INVENTOR. firwsi'ead 6% Geiz' BY M, W,

A. G. GETZ ROLLS FOR CORRUGATING METAL STRIPS Nov. 6, 1956 4 Sheets-Sheet 2 Original Filed March 23, 1951 INVENTOR; cv fi/zsi'eczd 6-1 66525 mY-MW,

Nov. 6, 1956 A. G. GETZ 2,769,479

ROLLS FOR CORRUGATING METAL STRIPS Original Filed March 23, 1951 4 Sheets-Sheet 3 INVENTORI. Q/ ZWIZSL QCZ G Get? Nov. 6, 1956 A. 6. GETZ 2,769,479

ROLLS FOR CORRUGATING METAL STRIPS Original Filed March 25, 1951 4 SLeets-Sheet 4 I IH. g IHIH' 33 1 -1:'

{I U I 28 l I 26 I "I II I! \\l// M N 1" hmw IN V EN TOR.

BY M,

Unite ROLLS For conauosrnso METAL ss Arnstead G. Getz, Lakewood, Ghio, assignor to The Bishop and Bahcock Manufacturing Company, Cleveland, Ohio, a corporation of Ohio 5 Claims. (Ci. 15377) This invention relates to machines metal strip to be used in cores of heat exchange units, and has to do with rolls for use in such machines.

It is known, in constructing cores of the character referred to, to provide metal strips formed with corrugations or projections, usually of straight line contour, which strips when assembled in the core define between them air passages having interior projections for imparting turbulence to the air and assuring contact thereof with the metal of the core. The strips are formed of quite thin metal, such as electrolytic copper having a thickness of approximately .0035" and, under present practice, usually are formed to desired shape by subjecting them to pressure between opposed forming surfaces conforming to the desired contour of the ultimate form of the strip. During such forming operation the thin metal strip is subjected to considerable pressure between relatively moving opposed forming surfaces and is frequently torn or ruptured in the forming operation. That results in objectionable waste of metal and also necessitates care in designing the final form of the strip so as to reduce, as far as possible, wastage. As noted, the final form of the strip usually is so designed that the corrugations or projections thereof are defined by straight lines, with a view to reducing tearing of the strip and resultant wastage to a minimum. It has been attempted to produce strips having projections or corrugations defined by curved lines but, in general, the resultant wastage, due to rupture and tearing of the metal, when using the present methods above referred to, has been so great as to be prohibitive.

My invention is directed to the production of corrugated metal strip of desired final form without incurring the wastage of metal which occurs under the present practice above referred to. It is directed particularly to the production of corrugated metal strip provided with corrugations which are undulatory lengthwise, without subjecting the strip to forming pressure between opposed forming and pressure applying surfaces such as would be apt to cause rupture or tearing of the metal, as occurs under the present practice above referred to. I form the strip to approximately final form by pulling it about forming members or ribs extending in alternately opposite directions beyond the plane of the metal strip being operated upon, and spaced apart a distance materially greater than the thickness of the metal strip so as to avoid subjecting it to pressure between opposed forming surfaces. When the strip has been preformed in the manner stated, it is subjected to a final forming operation similar to the preforming operation, the height and spacing of the forming elements or ribs used in the preforming operation being so related to the height and spacing of the forming elements or ribs used in the final forming operation as to render available for the latter operation adequate metal such that any objectionable stretching or thinning of the metal in the final forming operation is avoided. In both the preforming operation and the final forming operation the strip is at no time subjected to for corrugating Patent forming pressure between opposed forming surfaces thereby eliminating risk of rupture or tearing of the metal strip from that cause. The preforming operation is accomplished by opposed members, conveniently corrugating rolls, provided with spaced apart forming elements or ribs of such height and spacing that, in the rotation of the rolls, the ribs of each thereof enter midway between the ribs of the other roll with clearance therebetween materially greater than the thickness of the metal strip. Preferably, the ribs are of undulatory formation lengthwise. During rotation of the rolls, the metal strip is drawn between them and is pulled about the ribs in contact with the radially outer edges only thereof so as to be formed into corrugations also of undulatory formation lengthwise, the metal strip being at no time subjected to forming pressure between opposed forming surfaces. The preformed metal strip passes from the preforming members or rolls to the final forming members, preferably also two opposed corrugating rolls similar to the preforming rolls but having the forming elements or ribs thereof of slightly less height and greater spacing than the ribs of the preforming rolls, to avoid any objectionable stretching of the metal in the final forming operation, as above explained.

My present invention is concerned more particularly with the corrugating rolls. Preferably two pairs of rolls are used-a pair of preforming rolls and a pair of final forming rolls. The rolls of each pair are provided with spaced ribs of undulatory formation lengthwise, with the crests of the undulations of each rib extending at least to, preferably overlapping, the crests of the two next adjacent ribs. The rolls of each pair are angularly off-set so that the ribs of one of the rolls enter midway between the ribs of the other roll. A metal strip passed between the rolls is thus provided with transverse corrugations or ribs which are undulatory lengthwise with the crests of the undulations of each rib extending to and preferably overlapping the crests of the undulations of the two next adjacent ribs. The metal strips thus corrugated may be used as spacers or separators between the water passages of the core of a heat exchange unit and provide undulatory passages therebetween for flow of cooling air, such air passages preventing straight flow of air through the core while providing for large volume of air flow and high turbulence assuring intimate heat exchange contact between the air and the metal of the core. It is also an object of my invention to provide rolls effective for corrugating metal strip without objectionable damage thereto, as above explained. The undulatory ribs of the rolls are formed as separate stampings having radially inner elements straight lengthwise of the ribs and inserted into lengthwise slots in the rolls, the ribs being removably mounted in the rolls by appropriate means. Further ob jects and advantages of my invention will appear from the detailed description.

This application is a division of my copending application for Means for and Method of Corrugating Metal Strip, Serial No. 217,228, filed March 23, 1951, now Patent No. 2,684,707, issued July 27, 1954. The corrugated metal strip produced by the machine, including the corrugating rolls, of said .copending application are, as stated therein, used in constructing cores of heat exchange units such as that disclosed in my then copending application, Serial No. 142,796, filed February 7, 1950, now Patent No. 2,594,008.

A description of the metal strip corrugating machine using the rolls of my present invention will be conducive to. a clear understanding of the construction and operation of the rolls and they advantages thereof. Accordingly, the description to follow includes a description of the machine and the rolls, with particular attention to the latter.

In the drawings:

Figure 1 is a side view, partly broken away, of a metal strip cornlgating machine. embodying the corrugating rolls of my invention; 7

Figure 2 is a side view of the machine of Figure 1, as seen from the side opposite to that shown in Figure 1, with' certain parts shown in the latter figure omitted;

Figure 3 is a sectional view, on an enlarged scale, taken substantially on line 33 of Figure l; I v

Figure 4 is' a side view, on an enlarged scale, of one of the forming elements or ribs of the performing rolls shown in Figure 3;

Figure 5 is a plan view of the rib shown in Figure 4;

Figure 6 is a side View, on an enlarged scale, of one of the ribs of the final forming rolls; 7

'Figure 7 is a plan view of the rib of Figure 6;

Figure 8 isa fragmentary plan view, on an enlarged scale, of the rib of Figure 7;

Figure 9 is a fragmentary end view, on an enlarged scale and partly broken away, of one of the preforming rolls and its associated shaft;

Figure 10 is a fragmentary semi-diagrammatic view, on an enlarged scale, showing in end view the two preforming rolls and metal strip passing between them;

Figure 11 is a view similar to Figure 10 but showing the final forming rolls;

Figure 12 is a fragmentary face view of the preformed corrugated metal strip produced by the preforming corrugating rolls; and

Figure 13 is a fragmentary face view of the corrugated metal strip produced by the final forming corrugating rolls.

The machine shown in Figure 1 comprises a suitable base or table 20 to which are secured two pairs of spaced uprights 21 and 22. Upper and lower preforming rolls 23 are rotatably mounted in the uprights 21, aligned lengthwise of table20 with upper and lower final forming rolls 24 As is shown more clearly in Figure 9 each of the preforming rolls23 comprises a cylindrical body 25 having an axial bore for reception of a shaft 26 on which body 25 is suitably secured, conveniently by means of keys 27. Body 25 is provided with a plurality of lengthwise slots uniformly spaced circumferentially thereof and opening through the ends and the outer circumferential face of body 25. The slots in body 25 receive forming elements or ribs 28, shown more clearly in Figures 3, 4 and 5, which are of undulatory formation lengthwise and are straight and of substantially uniform thickness radially of body 25 of roll 23. The ribs 28 preferably are formed of cold rolled steel and are milled off for the major portion of their height to provide spaced fingers 29 extending downward from the rib 28, between end fingers 30 of materially greater extent lengthwise of rib 28 than the fingers 29 and straight lengthwise of rib 28, the outer or upper portions of the fingers 30 providing straight terminal extensions of the rib 28. from what has been said, the fingers29 of ribs 28 extend As will be understood 7 2,769,479 (A V g l project radially outward beyond body 25 of the respective rolls 23 a distance appreciably less than the space between the bodies 25 of rolls 23, and'are rounded at their outer edges, as shown more clearly in Figure 10. The rolls 23 are relatively off-set angularly so that in the rotation thereof the ribs 28' of each roll 23 enter midway between the ribs 23 of the other roll, with considerable clearance therebetween. Meshing spur gears 38*, secured on the corresponding end of shafts 26 of rolls 23, assure that both thereof will be rotated at the same speed, the gear ratio being appropriate to that end, while maintaining the proper angular relation between the rolls and also assuring that they will be rotated in opposite relation. Accordingly, when either of the preforming rolls 23 is rotated, the other roll will also be rotated at the same speed and in opposite relation, and the ribs 28 of the rolls will enter between each other as above explained, these ribs being of such height that the ribs of each roll at all times clear the ribs of the other roll during rotation of the rolls, as will be understood from what has been said.

A bevel gear 40 is secured on shaft 26 of the lower roll 23, at the opposite end thereof from the spur gear 38*, and meshes with a bevel gear 41 secured on shaft 42 of a speed reducing unit 43 of suitable known type, mounted on table 20 toone side of one of the uprights 21. A second shaft 44 of unit 43 is driven, through a suitable coupling 45 of known type, by shaft 46 of an electric motor'47 mounted on table 26. It will be clear, from what has been said, that when the motor 47 is in operation the two preforming rolls 23 are driven at the same speed and in opposite relation, it being understood that the unit 7 43 is selected to drive the rolls 23 at appropriate speed.

The final forming rolls 24 are similar to the preforming rolls 23 and a brief description thereof will suffice. Each of the rolls 24 comprises a cylindrical body 40 keyed on a shaft 411 rotatably mounted in hearings in the uprights 22. The body 48 is provided with lengthwise slots opening through its ends and its outer circumference and receiving final forming elements or ribs 42 projecting radially beyond body 46*. Referring to Figures 6 to 8, inclusive, the ribs 42* preferably are formed of cold rolled steel, are of undulatory formation for the major portion of their length, and are milled off at opposite sides to provide spaced fingers 43 aligned with relatively wide end fingers 44' straight lengthwiseof rib 42 the upper portions of which provide stra'ight continuations or terminal elements of the rib 42*. Each of the fingers 44 is provided with a rectangular. notch 46 in its outer edge, these notches 46* receiving locking rings fitting therein and inr annular recesses in the ends of body 40, held in position by retaining plates secured to the ends of body 4fi as in the preforrning rolls 23.

The upper or radially outer edge of each rib. 42 is flat,

3 as shown more clearly in Figures 6 and 11, and each into the slots of body 25 of roll 23 for positioning the ribs e 28 thereon. Each of the fingers 30 is provided, in its outer edge, with a rectangular notch 31 which registers with a rectangular annular groove 32 in the end 'of the roll body 25. A locking ring 33 fits snugly ingroov'e' 32 and in the notches 31 of fingers 30, thus locking the ribs 28 tightly in position in the roll body 25. The ring 33 is retained in position by an annular plate 35 seating thereon and on the end of body 25 and secured to the latter in a suitable manner, conveniently by means of screws 36, As will be understood, there is a lockingiring 33 and plate 35 at each end of body 25 of roll 23. The end portion of shaft 26 of each of the rolls 23 is of reduced diameter and is rotatably mounted in suitable bearings 38, mounted in the uprightsll, as is shown more clearly in Figure 3. V 7

The ribs 28 are all of the same effective heightand undulation of rib 42 is provided at the outer side thereof with a boss or projection48 of approximately semielliptical shape in plan having an inner face 49 straight lengthwise of rib 42 and an outer face conforming to the curvature of the correspondingundulation of rib 42..

The effective height of ribs 42*, that isextent to which they project beyond the body, ofroll 40 to theflat upper edges thereof, but not including the bosses 48, is less than the effective height of the ribs 28 ofthepreforming rolls 23 by an amount equal to the height of bosses 48, the effective height of ribs 42% at the bosses48 being equal to theelfective height of theribs 28.,of preforming rolls 23; aswill becleanfromFigures ,4, 6, '10 and 11. Also, 7 the ribs 42 of the final formingrolls .24 are spaced somea what further apart than the ribs 28..of.-the preforming rolls 23, as shown -in Figures 10 and 11, for a purpose which will, appear later. e

.The effective heightor radial extent of the ribs 42 beyond bodies 40 ofthe finalforming rolls 24-is appreciably lessuthan the distancebetween bodies 40; as shown in- Figure 11. V The final forming rolls 24 are angularly off-set one half the distance between adjacent ribs 32 thereof so that the ribs of each roll, during rotation thereof, enter midway between the ribs of the other roll with clearance therebetween materially greater than the thickness of the metal strip operated upon. As will be understood from what has been said, the spacing and radial extent of the ribs 42 is such that there is at all times, during rotation of the rolls, ample clearance between the ribs thereof to guard against subjecting the metal strip to pressure between the ribs, which is also true of the preforming rolls, as above noted.

Meshing spur gears 50 secured on the ends of shafts 41 adjacent one of the uprights 22, assure that the rolls 24 will be driven at the same speed and in opposite direction and that the angular relation therebetween will be maintained. A sprocket wheel 52 is secured on shaft 26 of the upper preforming roll 23, at the opposite end thereof from spur gear 38. This sprocket wheel 52 has driving connection, through a sprocket chain 53, to a similar sprocket wheel 54 secured on shaft 41 of the upper final forming roll 24 at the end thereof opposite to spur gear 50. It will be seen that when the preforming rolls 23 are driven, the final forming rolls 24 are also driven, the rolls of each pair being driven at the same speed and in opposite relation and the rolls of both pairs being driven at the same speed and in the same relation, that is, the upper rolls are driven at the same speed and in the same direction and the lower rolls are driven at the same speed as the upper rolls and in the opposite direction relative thereto.

The two pairs of rolls are aligned for reception between them of the metal strip being operated upon. As the finally formed metal strip passes beyond the final forming rolls 24, it is cut to length by suitable cut-off means. Conveniently, two opposed cut-E blades 57 and 58 are slidab'ly mounted in slotted uprights, one of which is shown at 59, secured to table 20 in spaced relation transversely thereof. The upper blade 57 is pivoted at each end thereof, at 60, to a link 61 pivoted at its lower end, at 62, to the inner end of a lever 63 pivoted at its midpoint, at 64, on a bracket 65 secured to upright59 and extending rearwardly therefrom. The forward end of lever 63 is connected, by a pin and slot connection 66, to the lower blade 58. A tension spring 67 is anchored at its lower end to pivot 62 and at its upper end to upright 59. This spring 67 tends to straighten the toggle comprising the link 61 and the inner arm of lever 63, thus urging the upper blade 57 upward, such upward movement of blade 57 being limited to stop screws, one of which is shown at 63, threaded through a cross piece 70 connecting the upper ends of the uprights 59.

The lever 63 is provided with a downwardly extending arm 72 having ase ries of openings for adjustably attaching thereto the forward end of a rod 73 provided at its rearward end with a fork 74 fitting about hub 75 of a cam disc 76 secured on shaft 41 of the lower final forming roll 24, at the opposite end thereof from the spur gear 59. Thedisc 76 is provided with a nose 78 disposed to contact a roller 7E3 carried by rod 73, for moving the latter forward. In the forward movement of rod 73 the blades 57 and 58 are moved toward each other and are effective for severing the metal strip passing therebetween, as will be clear. When .the nose 78 passes out of contact with the lever 79, the blades 57 and 58 are returned to their normal positions shown in Figure l, by the tension springs 67, and the rod 73 is moved rearward into position with the roller 79 disposed for contact by nose 78, as shown. It will be seen that the cut-oif means is operated in timed relation to the rotation of the rolls, the timing being such that the finally formed strip passing from the rolls 24 is cut into lengths of predetermined and desired extent.

Two bracket arms 78*, slotted from their upper ends, are secured to and extend upwardly and rearwardly fromthe uprights 21. The arms 78 receive the ends of a 6 shaft 7% rotatably mounted therein and carrying a roll 80 of metal strip or ribbon 81 of appropriate width and thickness, this metalstrip commonly being quite thin, as above noted. In the operation of the machine. the metal strip 31 is drawn from the roll 80 and passes between the pairs of rollers 23 and '24 and thence through the cut-off means, as will be clear. Preferably, the arms 78 are provided with friction'surfaces contacting the sides of the roll 80 eifective for preventing free running thereof while not imposing sufficient drag on the roll to cause objectionable 'tensioning of the metal strip 81, thus assuring that the metal strip is drawn smoothly from theroll as required in the operation of the machine; As the metal stripiSl passes between the preforming rolls 23 it is pulled about the ribs 28 thereof, as shown diagrammatically in 'Figure 10,'and is corrugated transversely, the crests of the corrugations thus produced being rounded as shown. It will he noted that there is considerable clearance between the ribs and the metal strip pulled thereabout, and that at no .time is the metm strip subjected to forming pressure between opposed relatively moving pressure applying surfaces. The metal strip 81 conforms to the lengthwise formation of the ribs 28 as it is pulled thereabout, and the preformed strip leaving the rolls 23 is provided with corrugations 82 of substantially V cross section and of undulatory formation transversely of the strip for substantially the full width thereof, except for terminal elements 83 which are straight transversely of the strip; as shown in Figure 12. By avoiding subjecting the strip to pressure between opposed forming surfaces, 1 eliminate risk of tearing and rupture of the strip from that'cause, thereby elirninating wastage while also. rendering it possible to corrugate the metal strip at comparatively high speed with resultant increase in production. V

'Ihe preformed strip 81a passes from thepreforming rolls 23 over a supporting shelf 85 mounted between the pairs of uprights. 21 and 22 and extending therebetween. From the final forming rolls 24 the strip passes over a second shelf 86 supported between the uprights 22 and thence over two spaced shelves 87 carried by the uprights 59. In the passage of the preformed strip 81a between the final forming roll-s 24, the crests of the corrugations 82 thereof are flattened, the corrugations are slightly spread or opened up, and the bosses 43 move corresponding areas of the corrugations outward beyond the flattened crests. The resultant finally corrugated strip 81b is provided with'transversely extending corrugations 90 of undulatory formation for the major portion of their length and having straight terminal elements 91 trans versely of the strip, the corrugations 90 being provided at the outer side of each undulation thereof with a boss or projection 92 of relatively slight height having an inner surface straight transversely of the strip. By hav, ing the forming elementsor ribs 42 of the rolls 24 of less effective height than the ribs 28 of the preforming rolls 23, I render available adequate metal for forming the corrugations to final shape between the rolls 24 in the manner stated without subjecting the metal to appreciable or detectable stretching, thereby avoiding thinning of the metal to any objectionable or detectable extent. In the final forming rolls, as in the preforming rolls, the metal strip is formed by being pulled about the forming elements or ribs and is at no time subjected to forming pressure between opposed pressure applying forming surfaces, particularly during relative movement thereof. In that manner, I further guard against tearing or rupture of the metal strip with the advantages above noted.

Referring to Figures 3, l2 and 13, it will be seen tha the undulations of each rib formed in the metal strip overlap the undulations of the two next adjacent ribs. That eliminates any straight air passages between the ribs transversely of the corrugated metal strip and assures that, in a core having spacers or separators fabricated such metal strip, the cooling air will flow through tortuous passages between the undulatory ribs so asto create high air turbulence and assure intimate heat exchange contact of thejcooling air with the metal of the ,core. By having the ribs of the metal strip of undulatory form lengthwise, with the undulations thereof well rounded and merging smoothly'one into the other, flow V of cooling air between the ribs is unimpeded and large volume airflow adequate for cooling purposes is assured. V In orderto assure overlapping of the undulations of the rolls of each pair are similarly formed andspaced, and

the rolls of each pair are angularly oif-set so that the ribs of each roll enter midway betweenthe ribs of the other roll, as above described. Accordingly, in the rotation of the rolls of each pair, the undulations of the respective ribs of each roll entering between two ribs of the other roll overlap the undulations of those two ribs of such other roll. The metal strip is thus provided, at'thei'opposite faces thereof, with transverseundulatory ribs and the undulations of each rib at each face of the strip ex-- tend at least to, and preferably overlap, the crests of the undulations of the two next'adjacent ribs, as and for the reasons above explained. Preferably, the undulations of the two next ribs, as above stated. Within the broader V aspects of my invention, however, the ribs of the respective rolls may be so disposed that a straightline connect-. ing the crests of the undulations at each side of each rib will be in close proximity to astraight line connecting the crests of the undulations at the near side of each of the next two adjacent ribs, the space between such straight lines'not being greater than, preferablysomewhat less than, the thickness of. the metal strip to be corrugated. In other words, the planes of. the crests of the undulations of adjacent'ribs of therolls should not berspaced'apart a distance greater than the thickness of the metal to be worked, to assure that the crests of adjacent ribs formed in the metal strip will at least extend to a common plane,

in order not' to provide a straight path foriairflow between the ribs. .It is preferred, however, that theundulations .of therespective ribs formed in the metalstripoverlap to some extent the undulations of the two next adjacent ribs, as previously explained and shown.

The finally formedlengths of metal strip are used. in

' constructing cores of heat'exchangers, such as automobile tween water wall strips defining between them water passages, the latter strips having transverse ribs upon which the corrugations of the air passage strips seat,

being positioned thereon bythe bosses 92 of Figure 13. The opposed corrugatedair passage strips define between them undulatory air passages which imparthigh turbulence to air flowing therethrough, as well as large area of contact between the airand the metal, thereby attain ing highefiiciency'in heat transfer. 7

It will be understood that changes in detail may be made and l intend to include all such variations, as fall tion in which 'the preferred form-only ofmy invention;

lengthwise projecting radially. outward beyond ,said Troll body'and fingers extending radiallyjnwardfromsaid rib alignedlengthwise thereof and seating in the correspondl 'of each rib of the respective rolls overlap the undulations r a s a a 7 within the scope-of the appended claims, inthis applicm has been disclosed. 7'

claim:

1.' In a roll for corrugating m'etal a body having I lengthwise slots. opening through its circumferential sur: face, and corrugating members securedl'in said slots respectively comprising a'radially outer portion providing a rib of undulatory formation lengthwise projecting radially outward beyond said. roll body and radially inner positioning means substantially'straight lengthwise of said rib and seating in the corresponding one of said slots.

2. In a roll for corrugating metal strip, a body having lengthwise slots opening through its circumferential surface, and corrugating'members secured in said slots respectively comprising a rib of nndulatory formation ing'one of'said slots.

3. In aroll for corrugating metal strip, a body having, lengthwise slots opening through its circumferential and end surfaces, corrugatin'g' members respectively compris-.

ing a rib of undulatory formation, lengthwise projecting radially outward, beyond said roll body. and fingers extending radially inward fromsaid rib aligned lengthwise thereof and seating in thecbrreSPO'nding one ofjs'aid slots,

certain of said fingers beingat the ends 'of 'said rib and having j notches intheir outer edges, and locking rings secured to the en'cls'of said roll body andfseating in said V notches.

4. In a roll for corrugating metal strip, a body having straight lengthwise slots of substantially uniform 'width opening through. its 1 circumferential surfa'ce, and corru gating members secured insaid slots and of approxi- 'mately thesame thickness a'sthe width'of the respective slots, saidcorrugating members respectivelycomprising aribbfundulatory formation}lengthwiseprojecting radially outwardbeyond said roll body and fingers extending radially inward from'said rib aligned lengthwise thereof and seating in the corresponding one of said slots.

'5. In a roll for corrugating metal strip, a body'havingg 1 uniformly spaced lengthwise slots'f o'f substantially uniform width and substantially parallel with its. axis and opening through its circumferential surface," and corrugating members secured in said slots and'of'approximately the same thickness'as the width 'of the'respectiveslots, said corrugating members respectively comprising a rib of un dulatory formation lengthwise projecting radially out ward beyond said roll body and fingers extending radially inward from said 1 rib aligned lengthwise thereof and seating'in thecorresponding one of said slots.

' References Cited in the file or patent UNITED STATES- PATENTS 1,211,818 Bradley Jan. 9, 1917 1,225,730 Garguilo May 8, 1917 1,450,351 7 Beran Apr. 3,1923 1,868,302 Auger July 19,1932, 2,079,995, Hodgkins May 11, 1937 2,205,343 7 'Carelli V V June 18, 1940 2,290,608 Evans Ju1y 21, 1942.

'FOREIGN'PATENTS j 22,533 Great Britain 1912' Australia May 15, 1947 r 

